The fluorescent lamp is the most widely utilized light source in the world for general illumination, primarily because of its relatively low initial cost and its efficacy: i.e., its light output relative to its power input, usually expressed as lumens per watt (LPW). Nevertheless, for home use, the fluorescent lamp has not taken precedence over the incandescent lamp. Many reasons have been advanced for this lack of acceptance, among them the poor color rendition of some fluorescent lamps and their need for a ballast. However, one of the major disadvantages lies in the fact that a fluorescent lamp is a linear source whereas an incandescent lamp can almost be considered a point source. The typical fluorescent lamp has a length of from 18" to 8' and is somewhat cumbersome to work with.
With the increasing cost of energy, attempts have been made to overcome the latter difficulty. One of these attempts has utilized a plurality of fluorescent tubes having one or more smaller tubes connecting the ends of the fluorescent tubes to provide an arc path. Such lamps are shown in U.S. Pat. No. 3,501,662. Large, "U" shaped lamps such as those shown in U.S. Pat. Nos. 3,602,755; and 2,401,228; and triple bend lamps such as shown in U.S. Pat. No. 4,347,460 exemplify other attempts.
Still other attempts are shown in U.S. Pat. Nos. 4,208,618; 4,191,907; and 4,524,301, filed Sept. 30, 1982 and assigned to the assignee of the instant invention.
While each of these proposals has its own advantages, disadvantages also exist. The previous forms of multiple tubing lamps are expensive to produce and difficult to handle during manufacture.
Many types require expensive, custom made partitions and/or require large numbers of hermetic seals. Multiple bend tubes require large outlays for manufacturing equipment which adds to the cost of the final lamp.
Yet another type of compact light source is exemplified by a fluorescent lamp comprising an hermetically sealed outer envelope containing an arc generating and sustaining medium. Positioned within this outer envelope is an assembly comprised of a plurality of elongated glass tubes coated on their interior surface with a phosphor. All of the interior surfaces are open to the medium. The tubes have first and second ends and the assembly has first and second arc directing means operatively associated with the first and second ends of the tubes to provide a continuous arc path therethrough. An electrode is positioned at both ends of the arc path and means are provided for making electrical connection to the electrodes.
In an alternate embodiment, the assembly comprises a pair of U shaped tubes each having an electroded end and an open end. An arc directing means is operatively associated with the ends of the tubes and includes an arc director which connects the open end of the tubes.
Compact fluorescent lamps built according to the above provide many improvements over the prior art. Custom-made partition structures are avoided as are multiple hermetic seals. Also, since either straight tubing or simple U shaped tubes are employed, complex machinery for making multiple bends is also obviated and lamps made in accordance with this invention are economical to fabricate.
Pending applications bearing U.S. Pat. Nos. 4,536,678; 4,527,088; and 4,527,089, filed Apr. 1, 1983 and assigned to the assignee of the instant invention, disclose features of the latter two lamps and the appropriate teachings of these applications are hereby incorporated herein by reference.